In recent times, dual clutch transmissions and dual clutches have received substantial interest in a renewal of use. The reason for this is that such transmissions and clutches, in an automization of a transmission provide an ease of shifting, which is similar to the shifting of familiar transmissions possessing a torque converter. However, these mechanisms allow much to be desired as to the degree of efficiency in their operation. An essential advantage of the dual clutch transmission over conventional automatic transmissions with direct shifting, is related to a corresponding coordination between the transmission gear selection and the transmission input shaft. The act of shifting with the invented dual clutch takes place while the motor driving force remains active, that is, the driving power is still functioning during the execution of shifting from a gear stage assigned to one of the individual transmission input shafts to an assigned gear stage of the other transmission input shaft.
In accordance with a given gear stage, and other gear stages which can be involved, a relatively high degree of synchronization operation must be expended. Let it be noted here, as to the said gear stage, that, relative to the present gear to be abandoned and the desired gear to be shifted to, under certain circumstances, a driver will not choose to shift between gears which are not successive to one another in a manner free of driving power interruption, or torque drag. In the proposal here offered, among others, the dual clutch itself is active in the support of the synchronization—as far as possible—that is to say, it initiates the synchronization itself by means of appropriate activation of the clutch assignment. For example, DE 199 39 819 C1 discloses, in a special way, a procedure which favors internal transmission synchronization. The said internal synchronization cannot be eliminated, since the procedure presented in the said patent text only borders on the conventional synchronization rings and does not have the capability of accelerating above the motor speed of revolution currently in use.
Another possibility is, to provide synchronizing apparatuses of the conventional type (these being, for example, common synchronization rings and the like), but allowing a safety factor for a higher degree of loading in accord with the synchronous operation to be carried out by the transmission. This arrangement, however, must be executed with some attention to a relatively greater installation-space and finally, the conclusion is made, that such synchronization devices of the conventional kind are not to be considered the “optimum” for the intended use.
Another approach stresses the provision of special synchronization devices, which enable a transmission of torque between a first gear train shaft governing at least one set of gear train stages (for example, the even numbered forward gear stages) and at least a second gear train shaft to which is assigned another set of gear stages (for instance, the odd forward traveling gear stages). In this respect, DE 44 36 526 A1, discloses a synchronization of a dual clutch transmission, wherein, a transmission is proposed, on the basis of an additional shaft and gear pairs assigned thereto. DE 44 36 526 A1 teaches that the successive gear stages are to alter by a factor of “q”. On this account, this arrangement is not suited for optional dual clutch transmissions. Because of the additionally required shaft, this transmission must be built even larger in the radial direction.
DE 34 17 504 A1 teaches additionally, of a synchronizing device based on multi-disk brakes in combination with a planetary gear set, which possesses a rotating shaft situated at a distance from and parallel to, the input shaft of the transmission. An additional planetary gear set is installed, which is coaxial to, or is on the same axis as the input shaft. This serves for the doubling of the gear stages before a 3-shaft-gear stage component, which can be shifted in or out by means of a shiftable clutch. The said shiftable clutch can also serve as a start-up clutch and is designed as a type of dual clutch. The said planetary gear set, which is provided for synchronization purposes and is not coaxial with the input shaft train, serves only for upward acceleration in regard to synchronization. For the braking operation, again in regard to the synchronization, the previously mentioned disk braking is employed.
Conversely to the above, the purpose of the invention is to create a dual clutch transmission with coaxial input shafts, which possesses a central synchronization device, which is compactly built, and without unwieldy mechanical attachments, and can be integrated into the transmission. The invented synchronization device, in addition, is to enable both an acceleration as well as a braking of a respective gear train shaft, and indeed—at least in a preferred development—both in regard to gear stages assigned to a first transmission input shaft and in regard to the gear stages assigned to the other transmission input shaft.